1. Field of the Invention
The present invention relates generally to radio communication effected using impulse radio. Still more particularity the present invention provides a method for mitigating adverse effects of electromagnetic interference in communicating using impulse radio wherein transmission rates (bit rates), signal strength, packet sizes and frequency of packet repetition, and other parameters associated with conveying a transmission message using impulse radio can vary according to the effect that interference may have upon impulse radio transmission quality.
2. Related Art
Recent advances in communications technology have enabled an emerging, revolutionary ultra wideband technology (UWB) called impulse radio communications systems (hereinafter called impulse radio).
Impulse radio was first fully described in a series of patents, including U.S. Pat. No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057 (issued Mar. 14, 1989), U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990) and U.S. Pat. No. 5,363,108 (issued Nov. 8, 1994) to Larry W. Fullerton. A second generation of impulse radio patents include U.S. Pat. Nos. 5,677,927 (issued Oct. 14, 1997) to Fullerton et al; and U.S. Pat. No. 5,687,169 (issued Nov. 11, 1997) and U.S. Pat. No. 5,832,035 (issued Nov. 3, 1998) to Fullerton. Theses patent documents are incorporated herein by reference.
Uses of impulse radio systems are described in U.S. patent application Ser. No. 09/332,502, entitled, xe2x80x9cSystem and Method for Intrusion Detection Using a Time Domain Radar Array,xe2x80x9d and U.S. patent application Ser. No. 09/332,503, entitled, xe2x80x9cWide Area Time Domain Radar Array,xe2x80x9d both filed the same day as the present application, Jun. 14, 1999, both of which are assigned to the assignee of the present invention, and both of which are incorporated herein by reference.
Basic impulse radio transmitters emit short pulses approaching a Gaussian monocycle with tightly controlled pulse-to-pulse intervals. Impulse radio systems typically use pulse position modulation, which is a form of time modulation where the value of each instantaneous sample of a modulating signal is caused to modulate the position of a pulse in time.
For impulse radio communications, the pulse-to-pulse interval is varied on a pulse-by-pulse basis by two components: an information component and a pseudo-random code component. Unlike direct sequence spread spectrum systems, the pseudo-random code for impulse radio communications is not necessary for energy spreading because the monocycle pulses themselves have an inherently wide bandwidth. Instead, the pseudo-random code of an impulse radio system is used for channelization, energy smoothing in the frequency domain and for interference suppression.
Generally speaking, an impulse radio receiver is a direct conversion receiver with a cross correlator front end. The front end coherently converts an electromagnetic pulse train of monocycle pulses to a baseband signal in a single stage. The data rate of the impulse radio transmission is typically a fraction of the periodic timing signal used as a time base. Because each data bit modulates the time position of many pulses of the periodic timing signal, this yields a modulated, coded timing signal that comprises a train of identically shaped pulses for each single data bit. The impulse radio receiver integrates multiple pulses to recover the transmitted information.
In a multi-user environment, impulse radio depends, in part, on processing gain to achieve rejection of unwanted signals. Because of the extremely high processing gain achievable with impulse radio, much higher dynamic ranges are possible than are commonly achieved with other spread spectrum methods, some of which must use power control in order to have a viable system. Further, if power is kept to a minimum in an impulse radio system, this will allow closer operation in co-site or nearly co-site situations where two impulse radios must operate concurrently, or where an impulse radio and a narrow band radio must operate close by one another and share the same band.
In some multi-user environments where there is a high density of users in a coverage area or where data rates are so high that processing gain is marginal, power control may be used to reduce the multi-user background noise to improve the number of channels available and the aggregate traffic density of the area.
Other sources of noise, or electro magnetic interference, may also interfere with efficient communication using impulse radio technology. In communicating voice messages, data messages, control messages, or other types of messages, interference causes problems by corrupting information intended to be conveyed by the transmission message.
There is a need for mitigating the effects of electromagnetic interference, or noise, in communication using impulse radio.
In particular, there is a need for mitigating the effects of electromagnetic interference having various characteristics in communication using impulse radio.
A method for mitigating adverse effects of interference in impulse radio communication is disclosed. Transmission rates (bit rates), signal strength, packet sizes and frequency of packet repetition, and other parameters associated with conveying a transmission message using impulse radio may be varied advantageously to mitigate the effects of electromagnetic interference, whatever the source of the interference may be. The impulse radio communication conveys a transmission message from a transmitting station to a receiving station displaced from the transmitting station. The transmission message includes an information payload and overhead information. The interference has an expected occurrence period. The method comprises the steps of: (a) conveying the transmission message in a plurality of transmission packets; (b) repeating conveyance of selected packets of the plurality of packets; the conveying and the repeat conveying making up a repeat transmission package; and (c) conveying the repeat transmission package a plurality of times at a repeat conveyance period greater than twice said expected occurrence period.
The impulse radio communication may convey a transmission message from a proximate transmitter to a distal receiver, and include receiving a reception message by a proximate receiver from a distal transmitter. In such a duplex impulse radio communication system, the method comprises the steps of: (a) providing receiver-interference indications by the distal receiver to the proximate transmitter regarding interference conditions at the distal receiver; the receiver-interference indications including time indicators generally denote interference events; the interference events include a degeneration time when the interference conditions begin to unacceptably degrade the impulse radio communication, and include a regeneration time when the interference conditions return from unacceptably degrading the impulse radio communication to less than unacceptably interfering with the impulse radio communication; (b) mathematically manipulating the receiver-interference indications to determine predicted noise periods; the predicted noise periods are time periods during which the interference conditions are predicted to unacceptably degrade the impulse radio communication; and (c) operating the proximate transmitter to convey the transmission message according to at least one of the following criteria: (1) avoiding conveying the transmission message during the predicted noise periods; (2) effecting the conveying the transmission message at a higher conveying power during the predicted noise periods; (3) varying error detection coding in the transmission message during the predicted noise periods; and (4) retransmitting at least a portion of the transmission message during periods following the predicted noise periods. The choices for operating criteria may further include: (5) avoiding conveying the transmission message when the receiver-interference is present in an interference strength greater than a first predetermined interference strength; (6) effecting the conveying the transmission message at a higher conveying power when the receiver-interference is present in an interference strength greater than a second predetermined interference strength; (7) varying error detection coding in the transmission message when the receiver-interference is present in an interference strength interference strength greater than a third predetermined interference strength; and (8) retransmitting at least a portion of the transmission message after the receiver-interference has been present in an interference strength greater than a fourth predetermined interference strength and has subsided to an interference strength less than a fifth predetermined interference strength. Other operating criteria are also appropriate and are discussed in greater detail later herein.
Some noise, or interference, may be periodic in nature, with a constant period or with a period that varies over time (i.e., quasi-periodic). Such periodic or quasi-periodic noise may be substantially predicted, at least within a limited time period. Other electromagnetic interference may be intermittent and less predictable. Usually no one type of interference occurs alone; most likely an impulse radio communication system will encounter a variety of interference, having varying periodicity or unpredictability, varying strengths, and other varying parameters.
It is therefore an object of the present invention to provide a novel method for mitigating adverse effects of electromagnetic interference in impulse radio communication.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.